Yesterday I bought and installed a 120mm (main system fan) and an 80mm (power supply) to replace the loud stock fans. After this it won't boot at all. When I press the front power button it just powers up for 1-2 seconds and then shuts right down again.

I tried taking out the mobo battery then pressing the pmu reset button just once and leaving it overnight. Then this morning I put the battery back in plugged power back in and tried to power it up. Same problem..

I have also tried unplugging the drives and new fans but still no go.

Any ideas or tips?

For the record its a G4 400 with a G4 1GHz upgrade, 1GB RAM, 2x80GB HD, and a DVD-RW

sounds like the g4 is looking for the psu fan certain older computers are rigged to there fans like dell computers for example if you have a case fan go out and try to replace it without a dell certified fan the computer will start and say on the screen the system fan is damage or not responding system will shut down in 2 sec..

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